This application discloses an invention that is related, generally and in various embodiments, to a method for smoothing input current to a power delivery system having regeneration capability.
Power delivery systems such as AC motor drives are generally available as either a fully regenerative system or as a non-regenerative system. For non-regenerative systems, input power flows from an input power source to the load, and power produced by the load is blocked from flowing back to the input power source. In fully regenerative systems, input power flows from an input power source to the load, and the power produced by the load may flow back to the input power source.
It is known in the art for such fully regenerative systems to comprise an active front end to control regenerative current. However, active front ends may tend to cause some level of distortion of the incoming AC power. To reduce the distortion and smooth the input current on each leg of the AC input, it is also known to utilize line reactors on each leg of the AC input. However, the line reactors tend to be a relatively bulky and expensive solution to the distortion problem.
For many applications, only a portion of the power produced by the load is required for purposes of braking, etc. For such applications, a regenerative system generally provides much more regeneration capability than is required. Accordingly, most regenerative systems are not very cost-effective for applications which require limited regeneration capability.
To realize a drive with limited regeneration capability, it is known to configure a drive with a combination of regenerative and non-regenerative cells. For example, U.S. patent application Ser. No. 11/419,064 (the '064 application) discloses such a drive. The drive disclosed by the '064 application may be configured to have varying levels of regeneration capability by varying the number of regenerative versus non-regenerative cells in the drive, and each regenerative power cell may comprise an active front end that comprises switching devices controlled by pulse width modulation. Although the drive disclosed in the '064 application provides a cost-effective solution for applications requiring limited regeneration capability, any use of line reactors therewith to reduce any distortions caused by the active front end unnecessary adds to the size and cost of the system.